Broadband Underwater Acoustic Transducer

ABSTRACT

An efficient, broadband, underwater acoustic transducer having nominally a quasi-omnidirectional radiation pattern is realized with a plurality of thin walled radially vibrating spherical piezoelectric transduction elements aligned axially. Each spherical transduction element is progressively smaller in diameter so as to enhance the combined frequency coverage and achieve the desirable radiation pattern. The transduction elements may be excited individually, or together electrically in series or in parallel combinations.

STATEMENT OF GOVERNMENT SUPPORT

This invention was made without government funding.

RELATED APPLICATION(S)

None.

FIELD OF THE INVENTION

The present invention relates to underwater acoustic transducers, moreparticularly, to broadband acoustic sources.

BACKGROUND OF THE INVENTION

Underwater acoustic transducers with wide bandwidth are desirable forunderwater communication, sonar, or noise, signal-making and jammingapplications. It is well known to those skilled in the art, that abroadband transducer may be achieved by a plurality of cylindricaltransducers to cover a desired frequency range, however in comparisonwith the subject approach, the former broadband transducers provideoutward radiation that is largely directional.

Many broadband electroacoustic transducers have been described using aplurality of cylindrical ring transducers elements each having differentresonance frequencies to achieve a broadband coverage. For example U.S.Pat. No. 2,438,927 by Krantz describes a plurality of magnetostrictivetransducers aligned coaxially in decreasing size. Such an approachemploying piezoelectric ceramic elements is common today to thoseskilled in the art whereby a sound is radiated predominantly in adirection radially outward to achieve an omnidirectional radiation inone plane. Such a beam pattern maybe considered toroidal in shape. U.S.Pat. No. 4,916,675 by Hoering also describes a broadband acoustictransducer by using a plurality of transducer rings although of the samediameter each having different resonance frequencies. U.S. Pat. No.4,439,847 by Massa describes a means to achieve a broadbandelectroacoustic transducer employing a plurality of cylindricaltransduction elements whereby the use of reflectors causes the primaryradiation to be directed on axis of comprising coaxial elements. Such abeam may be described as conical. U.S. Pat. No. 6,215,231 by Newnham et.al. describes a electroactive ceramic hollow sphere having access holesto enable the passage of instrumentality. U.S. Pat. No. 6,768,702 byBrown and Aronov describes obtaining broader bandwidth directionalelectroacoustics transducers by combining the use of multimodeexcitation of cylinders (or spheres) with conformal acoustic baffles.

SUMMARY OF THE INVENTION

This subject invention relates to electroacoustic transducers and morespecifically with extending the bandwidth of an underwater transmittingtransducer. In the preferred embodiment, the electroacoustic transduceris comprised of a plurality of spherical-shell transduction elementseach producing more omnidirectional and uniform radiation pattern.Radially polarized spherical piezoceramic elements have relatively higheffective electromechanical coupling coefficients resulting in broadbandwidth.

An efficient, broadband, underwater acoustic transducer having nominallya quasi-omnidirectional radiation pattern is realized with an electricalconnection of a plurality of thin-walled radially vibrating sphericalpiezoelectric transduction elements aligned axially. Each sphericaltransduction element is progressively smaller in diameter so as toenhance the combined frequency coverage and to provide a means forsufficiently separation of elements to promote radiation.

Each spherical transducer element is progressively smaller in diameterso that when enclosed in a suitable housing or encapsulation, thebroadband transducer takes on a streamlined or hydrodynamic shape sothat it may become the nose of a small diameter underwater vehicle.

According to the method embodiments of the present invention, theresulting transducer may be encapsulated in a suitable hydrodynamicshape and have means for its connection through a suitable basestructure for attachment to a suitable platform.

A further object of the invention is to encapsulate the above describedmulti-element transducer array within a hydrodynamic or streamlinedmolded shape of sound transmitting material to allow sound transmissionto the surrounding immersion fluid.

Another object of this invention is to produce a broadband underwatertransducer that has high efficiency over a wide frequency band as greatas one or two octaves for operating above the frequency range about 5kHz.

Another object of the invention is to utilize thin-walled sphericalshells having wall thickness of the order 10+/−5% of their radii inorder to achieve a wide bandwidth for each element in the array.

According to method embodiments of the present invention, a method ofelectrical connection is described to allow individual elements to beexcited or combinations of said elements excited simultaneously.

According to method embodiments of the present invention, individualelements may be selectively excited in particular fundamental lowerorder modes of extensional vibration or combinations thereof.

According to method embodiments of the present invention, the broadbandtransducer consisting of multiple thin walled piezoelectric sphericalshells, can be encapsulated as a single structure and made electricallyinsulated from the fluid of immersion by suitable encapsulation,molding, or containment.

According to the method embodiments the broadband transducer attached tosaid suitable platform may be in the form of a mobile submersiblevehicle where said combination of broadband transducer form a means forproviding broadband acoustic communications, broadband sonar, orbroadband acoustic signaling or interference.

According to the method embodiments said broadband transducer operatingas said countermeasure may faithfully convert suitable electricalsignals of deterministic, random, continuous, pulsed, discrete origininto acoustic signals in the medium in which it is immersed.

According to the method embodiments individual thin-walled sphericalshells may be substituted with thin-walled piezoelectric cylinders, sothat said broadband transducer consists of a compact combination ofspherical and cylindrical radiators.

According to the method embodiments said broadband transducer may beoperated in transmit, receive or simultaneously in duplex modes ofoperation.

According to the method embodiments said broadband transducer comprisedof individual spherical and/or cylindrical elements may have holes inthe distal polar surfaces to permit the passage of a tube, said tubepermitting the passage of a propeller shaft to provide means forpropulsion of a suitable platform.

According to the method embodiments said broadband transducer comprisedof individual spherical and/or cylindrical elements may have means topermit the interior of the hollow spherical or cylindrical transductionelements to be used for housing accompanying electronics and/orinductive tuning elements.

Further features, advantages and details of the present invention willbe appreciated by those of ordinary skill in the art from a review ofthe figures and a careful reading of the detailed description of thepreferred embodiments that follow, such description being merelyillustrative of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a frequency response curve showing the transmit pressure perunit volt response as a function of frequency for a broadband transducerconsisting of three electroacoustic transduction elements.

FIG. 2 is an illustration, cross sectional view, of an embodiment of thebroadband transducer consisting of a plurality (3 shown) spherical shelltransducers.

FIG. 3 is an illustration, cross-sectional view, of an embodiment of thebroadband transducer comprising both spherical shell and cylindricalshell transduction elements, said elements in axial alignment, with saidcylindrical shell elements at the base of the broadband transducer andwith said spherical shell elements at the apex of said broadbandtransducer.

FIG. 4 is an illustration, cross-sectional view, of an embodiment of thebroadband transducer comprising both spherical shell and cylindricalshell transduction elements, said elements in axial alignment, with saidcylindrical shell element(s) at the apex of the broadband transducer andwith said spherical shell element(s) at the base of said broadbandtransducer.

FIG. 5 is an illustration, cross-sectional view, of the broadbandtransducer wherein a means for including accompanying electronics and/ortuning elements in the interior of said transduction elements.

FIG. 6 is an illustration, cross sectional view, of an embodiment of thebroadband transducer with provisional means to include a propulsionshaft permitted to pass through the transducer.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings to fully convey the scope of theinvention to those skilled in the art.

In FIG. 1, the transmit pressure response per unit applied voltage or socalled TVR of broadband acoustic transducers is shown comprised of theresponse of a plurality of electroacoustic transduction elements soaligned in frequency space as to provide a suitable coverage of a broadrange of frequencies. Each response labeled as 1A, 1B, 1C correspondswith the response from an individual electroacoustic transductionelement. The numbers on both ordinates are arbitrarily chosen. Thehorizontal ordinate depicting frequency is presented in a logarithmicscale. The transducer elements are designed to have resonancefrequencies and quality factors to provide broad frequency coverage.

In FIG. 2, a broadband acoustic transducer is realized by thecombination of a plurality of spherical shell transduction elements(three are shown 1A, 1B, 1C). The broadband acoustic transducer mayinclude a provision to include a suitable mounting fixture that allowsthe passage of electrical wiring 3 which are in turn connected to theindividual transduction elements. The broadband acoustic transducer isoperable underwater by a suitable encapsulation, molding, or enclosureas shown by element 4, said element may take the form of a streamlinedor hydrodynamic shape to reduce drag forces when operated in theimmersion fluid while moving. The individual transduction elements maybe connected electrically in parallel or series or remain separatelyselectable.

In general, the broadband acoustic transducer in FIG. 2, 3, 4, 5, 6 canbe deployed in a body of water and submerged to great depth due to thestrength of spherical shell or cylindrical shell bodies. The broadbandacoustic transducer may be attached to a suitable vehicle to provide asuitable means of propulsion and movement at speed and depth. Theencapsulated body 4 may also serve to protect the individualtransduction elements. The spherical shell transduction elements (1A,1B, 1C) may be individually comprised of hemispherical shell elementsglued together by suitable means or other suitable means know to thoseskilled in the art. The broadband acoustic transducer device may berealized with 2, 3, 4, 5 or more separate transduction elements. Eachindividual transduction element may be further wired in a manner toselectively excite a particular mode of vibration.

In some embodiments, as shown in FIG. 3, the broadband acoustictransducer may employ a single or multiple cylindrical transductionelement (5A, 5B) in place of one or more spherical-shell transductionelements. In some embodiments the spherical-shell element may be closelyaligned or partially contained by the cylindrical shell element in orderto realize a more compact structure.

Still in other variants the a spherical shell element may be located atthe base of said broadband acoustic transducers in relation to acylindrical element that is at the opposing end to achieve a compactdevice and form factor.

In some embodiments, as shown in FIG. 5, a means exists to allowassociated electronics or tuning elements (9A, 9B, 9C) to be containedwithin corresponding transduction elements whether cylindrical (5A, 5B)or spherical (1B) type.

In some embodiments, as shown in FIG. 6, a means exists to allow thepassage of an axisymmetric tube (7) permitting the passage of apropeller shaft (6) suitably sealed, which may in turn be connected to apropeller (8) to allow propulsion of said broadband acoustic transducerin conjunction with elements of an underwater vehicle.

1. A broadband acoustic transducer for operation in a fluid medium, comprising a plurality of spherical shell electroacoustic elements having provisions for electrical connection of said electroacoustic transducers.
 2. The broadband acoustic transducer of claim 1 wherein the plurality of electroacoustic transducers are encapsulated, molded, or booted so as to permit operation in an immersed fluid.
 3. The broadband acoustic transducer of claim 2 where said encapsulated, molded, or booted structure is made in a hydrodynamic shape, making a smooth transition from a smaller diameter to a larger diameter so as to reduce drag forces when said transducer is moving through said immersed fluid.
 4. The broadband acoustic transducer unit of claim 1 wherein said transducer is connected to supporting functional electronics to realize operation as a broadband communication device.
 5. The broadband acoustic transducer unit of claim 1 wherein said transducer is connected to supporting functional electronics to realize operation as an acoustic source, said acoustic source having the function to interfere with the presence of other acoustical signals or operation of other vehicles, so as to operate as an acoustic countering device.
 6. The broadband acoustic transducer unit of claim 1 wherein said transducer is connected to a mobile device with means for propulsion in said immersed fluid.
 7. The broadband transducer of claim 6 where a provision is made to permit a first access hole on one pole of the sphere and a second access hole in the opposing pole of the sphere and thereby made to permit the passage of a propeller shaft for means of propulsion.
 8. The broadband acoustic transducer unit of claim 1 wherein comprising elements may be electrically connected individually, in electrical series, or in electrical parallel combination.
 9. The broadband acoustic transducer of claim 1, where the inner and outer surfaces of said spherical shell electroacoustic element is electroded, said parts of said inner and outer electroded surfaces are further divided, where said divided surfaces are connected electrically so as to cause the excitation of the spherical shell into corresponding individual or combined modes of electromechanical induced vibrations.
 10. The broadband acoustic transducer unit of claim 1, where the inner and outer surfaces of said spherical shell electroacoustic element is electroded and divided, where said inner and outer surfaces are further divided in halves, said halves separated at the equator, where the means exists to selectively excite said transduction element in modes of vibration or their combination by selecting the amplitude and relative phase of electrical signals supplied to each hemispherical part, thereby selectively exciting corresponding modes of vibration in the spherical shell, the lowest mode of vibration corresponding to the uniform breathing mode and the first mode of vibration corresponding to cosinusoidal distribution of radial vibrations
 11. The broadband acoustic transducer unit of claim 1, where said transduction elements are acoustically baffled on a hemispherical part of the surface of said transducer element.
 12. A broadband acoustic transducer for operation in a fluid medium, comprising individual transduction elements, at least one of said elements is a spherical shell electroacoustic transducers element, and at least one of said elements is a cylindrical shell transducer element.
 13. The broadband transducer of claim 11 where a provision is made to permit the passage of a propeller shaft for said means of propulsion.
 14. A broadband acoustic transducer consisting of a plurality of cylindrical-shell transduction elements where a provision is made to permit the passage of a propeller shaft for means of propulsion.
 15. The broadband acoustic transducer of claim 1 whereby a means to include electrical elements inside electroacoustic elements in order to conserve space.
 16. The broadband acoustic transducer of claim 11 whereby a means to include electrical elements inside said electroacoustic elements in order to conserve space.
 17. The broadband acoustic transducer of claim 1 whereby said transducer is made weightless in said immersed fluid by suitable design considerations of voided cavities.
 18. The broadband acoustic transducer of claim 1 whereby the electroacoustic transducer is realized with a piezoelectric ceramic transduction material.
 19. The broadband acoustic transducer unit of claim 5 wherein a second broadband acoustic transducer is connected to opposing end of a suitable structure.
 20. The broadband acoustic transducer unit of claim 1 where the spherical shell electroacoustic element is realized by joining two hemispherical piezoelectric shells. 